1989: Sequence-tagged Sites, Another Marker

A sequence-tagged site (STS) is a unique stretch of DNA that polymerase chain reaction (PCR) can easily detect. STSs are very useful for making physical maps of human chromosomes. Creating a physical map is much like putting together a large puzzle, where the pieces of the puzzle are pieces of DNA made by cutting up chromosomes. PCR can be used to test whether STSs are present within different fragments of DNA and accurately assign the DNA fragments to their proper places on the chromosomes.